1. Filed of the Invention
The present invention relates to a dancer roll mechanism that is capable of controlling the tension to be applied to a web with high accuracy, and a web feeding apparatus that incorporates such a dancer roll mechanism.
2. Description of the Related Art
Heretofore, dancer roll devices have been used to control the tension to be applied to a web that is fed along. The dancer roll devices comprise a roll, a lever by which the roll is supported, and an air cylinder for adjusting the moment imposed on the roll through the lever. The air cylinder is supplied with air whose pressure is regulated by an electro pneumatic transducer based on an instruction given from a controller.
However, the air cylinder tends to cause a delay in its response to the instruction given from the controller. Consequently, the dancer roll device with the air cylinder is liable to suffer an error in controlling the tension to be applied to the web.
In addition, a back pressure developed when the air from the air cylinder is discharged via the electro pneumatic transducer and a resistance to the sliding movement in the air cylinder are also likely to bring about an error in controlling the tension to be applied to the web.
As a result, the dancer roll device with the air cylinder tends to fail to control the web tension with high accuracy.
It is therefore an object of the present invention to provide a dancer roll mechanism that is capable of controlling the tension to be applied to a web with high accuracy, and a web feeding apparatus, which incorporates such a dancer roll mechanism.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.